Speed regulator with distance regulating function

ABSTRACT

A speed controller for motor vehicles is provided, the vehicle having a distance regulating function, a locating system for detecting locating data for objects that are in front of the vehicle, and an evaluation device for determining whether a located object needs to be treated as a relevant target object in the vehicle&#39;s lane. The speed controller includes a monitoring module that is designed to detect, by reference to the locating data, a situation in which objects not detected by the locating system are within close range and, in this situation, issue a takeover prompt to the driver.

FIELD OF THE INVENTION

The present invention relates to a speed controller for motor vehiclesthat includes a distance-regulating function, a locating system fordetecting locating data for objects that are in front of the vehicle,and an evaluation device for determining whether a located object needsto be treated as a relevant target object in the vehicle's traffic lane.

BACKGROUND INFORMATION

Distance and speed controllers for motor vehicles are known in the artand are also referred to as ACC (“adaptive cruise control”) systems. Inthese systems, objects such as vehicles ahead that are in the sametraffic lane in which the controlled vehicle is traveling are detectedusing a locating system. The locating system can be a camera system or aradar system, using which the distance to the vehicle ahead and therelative speed can be measured. By using a direction-sensitive radarsystem or by relying on additional parameters such as the steering angleof the vehicle, the detected objects can be checked for plausibility sothat, for example, vehicles in the vehicle's own lane can bedistinguished from traffic signs or markings on the side of the road orfrom vehicles in other lanes. If a vehicle ahead in the same lane iswithin the locating range of the radar, the driving speed of thecontrolled vehicle is regulated through intervention in the vehicle'sdrive and braking systems such that a speed-dependent margin of safetyfrom the vehicle ahead is maintained. If, on the other hand, there is novehicle within the locating range in the same lane, then regulation to aspeed desired by the driver, which has been entered using a set command,is effected. An example of a regulating system of this type is describedin “Adaptive Cruise Control System—Aspects and Development Trends” byWinner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in SAETechnical Paper Series 961010, International Congress & Exposition,Detroit, Feb. 26-29, 1996.

Such ACC systems were generally used previously in relatively stabletraffic situations, which are characterized by relatively high vehiclespeeds and correspondingly large distances between vehicles, especiallyduring travel on superhighways or expressways. If the vehicle beingtracked as the target object decelerates to a standstill in a trafficjam, for example, and the speed of the vehicle equipped with the ACCsystem is also decreased accordingly, then the speed controllerautomatically shuts off at a specific limiting speed on the order ofmagnitude of about 20 km/h, and an acoustic prompt is issued to thedriver to take over the control of the vehicle and to decelerate thevehicle to a standstill. The reason for this shutoff is primarily thatthe detection range of the locating system has gaps in the close rangeso that, as the distances from the target objects decrease, the dangerincreases that an obstruction will not be detected and recognized, evenif it is in the same traffic lane.

For example, the detection range in radar systems is limited by thegeometry of the radar beam, which emanates divergently from the radarsensor and scans only a limited angle range so that the full width ofthe traffic lane is not detected until a certain distance in front ofthe vehicle is reached. Similar “blind spots” can also occur in camerasystems or other known locating systems.

An object of the present invention is to provide a speed controller thatmakes it possible to expand the range of application of the regulatingfunction to include low speeds, without having to make exaggerateddemands on the detection range of the locating system.

SUMMARY

The above object is achieved according to the present invention by amonitoring module which is designed to detect, on the basis of thelocating data, a dangerous situation in which objects not detected bythe locating system are in close range, and in this situation issue amanual takeover prompt to the driver.

The present invention facilitates, in the cases in which reduction inspeed to very low speeds or, if necessary, to a standstill, occursduring operation of the speed controller, a safe and reliable distanceregulation up to the point the vehicle comes to a standstill in spite ofthe gaps within the detection range of the locating system. In mostcases, the external vehicle that is selected as the target object fordistance regulation will remain within the detection range until bothvehicles have decelerated to a standstill. In these cases, there is noneed, even when the speed falls below the previously set limiting speed,for the speed controller to be shut off and the driver to be prompted tomanually take over. Special precautionary measures are necessary for thecases in which the tracked target object “disappears” from the detectionrange during reduction in speed and the associated reduction in distancebecause, for example, the two vehicles in the same traffic lane aremoving in such a way that they are offset laterally from one another bya relatively great distance so that the vehicle ahead ends up in theblind spot of the radar system as the distance decreases. However, thesesituations that require a takeover prompt to the driver may beidentified with a high degree of certainty based on prior history, i.e.,based on the locating data measured immediately before the loss of thetarget object. It is therefore possible to limit the takeover prompt tothese special cases.

The resulting expansion of the range of application of the speedcontroller results not only in a considerable increase in comfort forthe driver, but it also contributes to an increase in traffic safetysince the driver is relieved of distraction when driving up to the backend of a traffic jam and is thus able to pay more attention to what ishappening in the adjacent lanes, so that, for example, he is able torecognize earlier when a driver of a vehicle in the adjacent lane isplanning to change lanes and move into the safe interval between thevehicle and the vehicle ahead.

By avoiding unnecessary takeover prompts, the danger is also reducedthat, in the event of a takeover prompt of this kind, the driver willirritate the traffic behind him through an overreaction such as suddenand excessive braking. By continuing automatic regulation even at verylow speeds, it is also possible in this speed range to take fulladvantage of the fact that the locating system is able to detect changesin the distance and relative speed of the vehicle ahead significantlymore accurately and earlier than the driver himself can, so that afaster and more appropriate reaction to changes in the deceleration oracceleration behavior of the vehicle ahead becomes possible.

ACC systems may be supplemented by what has been referred to as a “stop& go” or “stop & roll” function, by which, in the event of a traffic jamor slow-moving traffic, not only automatic braking to a standstill, butalso starting up again and slow rolling in the traffic jam is automated.In conjunction with these functions, which may also be used ininner-city traffic, for example, the speed controller according to thepresent invention also proves to be particularly advantageous.

In an ACC system, or even in conjunction with the stop & go function,takeover prompts to the driver in the form of an acoustic and/or opticalsignal may also occur in other situations. In an ACC system, the amountof vehicle deceleration that is achievable through automaticintervention in the drive system or braking system of the vehicle isnormally limited to values that do not result in a significant decreasein comfort or decrease in nuisance to the traffic behind it. If thesystem recognizes that the deceleration that is attainable in this wayis not sufficient to avoid a collision with the vehicle ahead, then atakeover prompt is issued at that point, even in known systems. In thepresent invention, the takeover prompt has the same form as in theseknown systems so that the driver is not irritated by a variety ofunfamiliar signals but, instead, is faced with a harmonized,easy-to-interpret and familiar man-machine interface.

Even if the target object that is being tracked is lost after the speedof the vehicle has fallen below the limiting speed of 20 km/h, this doesnot necessarily mean that a takeover prompt to the driver must beissued. For example, the loss of the target object may simply be due tothe fact that the vehicle immediately ahead has changed lanes. Thissituation is also identifiable by reference to the measured locatingdata so that automatic regulation may also be continued in this case—ifnecessary, by selecting what had previously been the second closestvehicle ahead as the new target object.

In distinguishing between a change of lanes by the vehicle ahead and aloss of the target object, which requires a takeover prompt, it ispossible to rely on known functions that are already implemented inexisting ACC systems. For example, it is common in ACC systems havingdirection-sensitive radar for the lateral offset of the target objectrelative to the current straightline direction of the vehicle to becalculated in the evaluation device based on the directional anddistance data for the target object. By tracking the curve of thecyclically consecutive lateral offset measurements over time, it ispossible to determine whether the vehicle ahead has changed lanes ornot. In addition, data containing information about directional changesby the vehicle such as steering angle or measured yaw rate or yawacceleration may also be used, if necessary.

When a vehicle is equipped with an electronic stability program (ESP)for controlling dynamic behavior, then the vehicle may already have ayaw acceleration or yaw rate sensor. The data from this sensor may thenalso be used by the speed controller to detect and quantify directionalchanges by the vehicle. In particular, it is possible to calculate thecurrent curve radius of the vehicle from the yaw rate in connection withthe measured driving speed. In ACC systems, this information is used topredict the probable geometry of the traffic lane in which the vehicleis traveling so that even in the case of a curved road it is possible todetermine, in connection with the lateral offset measurements, whetherthe target object is in the same lane or in an adjacent lane. Likewise,it is also possible using these data to detect a lane change by thevehicle. For this purpose, for example, the directional change of thevehicle as measured by the yaw rate sensor may be compared with thechanges in the azimuth angle of one or several located objects.

If a lane change of the vehicle is detected at low speed (below 20km/h), then this indicates that the driver already intends to take overcontrol himself. Nonetheless, it may also be advisable for safetyreasons to issue the takeover prompt in this case.

In conjunction with the plausibility evaluation, for the purpose ofdetermining whether the target object is in the same traffic lane or inan adjacent lane, two evaluation numbers Pi and Pa are calculated insome ACC systems, numbers that specify the probability that the targetobject is inside (Pi) or outside (Pa) the same traffic lane. Theseevaluation numbers are continually updated as a function of thecyclically measured locating data, in which process the prior history isalso included, generally in the form of sliding averages. If the targetobject has been in the same traffic lane for some time, this isindicated by a high value for Pi and a low value for Pa. If the targetobject is then suddenly lost, then this indicates that the target objectis still in the same traffic lane and is no longer detected only becauseit is in the blind spot of the radar beam. In this case, the takeoverprompt is issued as a consequence. If, on the other hand, the vehicleahead changes lanes, then Pi decreases and Pa increases in the course ofthe lane change so that the difference between these evaluation numbersis reduced. If this difference is below a specific threshold value atthe instant when the target object is lost, then it may be assumed thatthe target object has left the traffic lane, and speed regulation may becontinued without issuing a takeover prompt.

The danger that a target object will disappear from the detection rangeeven though it remains in the vehicle's traffic lane is particularlygreat when traveling along a curve. If the target object is located onthe outer edge of the detection range relative to the curve, inparticular, it is to be expected that this target object will be lostwhen the distance from the target object is further reduced and/or whenthe vehicles exit again from the curve. In this case, it may beadvisable to issue a takeover prompt as a preventive measure, evenbefore the target object actually leaves the detection range.

In general, the tighter the traveled curve is, the larger theclose-range portion of the vehicle's traffic lane becomes that can nolonger be detected by the locating system. If the current curve radiusof the vehicle as calculated from the yaw rate and the driving speed isbelow a specific value, it may therefore be advisable to issue atakeover prompt even when there is no target object within the detectionrange—because the previously tracked vehicle changed to another lane ashort time before, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an ACC (Adaptive Cruise Control) system.

FIG. 2 shows a diagram illustrating a detection range of a locatingsystem of a vehicle equipped with the ACC system.

FIG. 3 shows examples of the loss of a target object from the locatingrange when traveling along a curve.

FIG. 4 shows a flow chart of a monitoring routine that is implemented inthe ACC system according to the present invention.

DETAILED DESCRIPTION

Since the basic design and mode of operation of a speed controller or anACC (adaptive cruise control) system for motor vehicles are known, FIG.1 shows only the most important components of a system of this type in asimplified block diagram. The heart of the system is an ACC module 10that intervenes in the motor vehicle's drive system 12 and brakingsystem 14 and, if the road is clear, regulates the driving speed to thedesired speed set by the driver. A locating system 16, in the form of adirection-selective multibeam radar mounted on the front of the vehiclein the example shown, measures the distances and relative speeds of thevehicles ahead and also the stationary targets that are within thedetection range of the radar. The locating system 16 also measures theazimuth angle of the detected objects relative to the currentstraight-line direction of the vehicle. The locating data measured bylocating system 16 for all detected objects is transmitted to anevaluation device 18 and there undergoes a plausibility evaluation inorder to determine for each detected object whether it is a fixedstationary target such as a traffic sign on the edge of the road,oncoming vehicles in the lane for opposing traffic flow, or vehiclesahead. In the case of vehicles ahead, a distinction is also made as towhether they are traveling in the same traffic lane or in an adjacentlane as the controlled vehicle. If at least one vehicle ahead is in thesame lane, evaluation device 18 selects the vehicle immediately ahead,i.e., the one the shortest distance away, as the target object.

For the plausibility evaluation, evaluation device 18 also receives thesignal of a speed sensor 20, which measures the speed of the vehicle,and the output signal of a yaw rate sensor 22, which gives the currentyaw rate of the vehicle. Stationary targets and oncoming vehicles may beidentified by comparing the positive or negative relative speed measuredby locating system 16 with the driving speed of the vehicle as measuredby speed sensor 20. From the measured distance data and azimuth angles,evaluation device 18 calculates for each detected object a lateraloffset at right angles to the current direction of travel of the vehicleusing trigonometric functions. By comparing this lateral offset with theknown typical width of a traffic lane, it is possible to determine (atleast in the case of a straight road) whether the detected object isinside or outside the vehicle's traffic lane.

Since, however, the lateral offset of the vehicle relative to the centerof the traffic lane is generally not precisely known, these decisionsinvolve certain uncertainties, so that only probability assessments arepossible. The latter are expressed by an evaluation number Pi for theprobability that the vehicle ahead is in the same lane, and anevaluation number Pa for the probability that the vehicle ahead is notin the same lane. Additional information, if any, such as the positionof road markings detected using a camera system or locating data fromradar reflectors set up along the road may be used to improve accuracy.

The signals of yaw rate sensor 22 are primarily used to predict theprobable curved shape of the vehicle's traffic lane on curvy stretches.For this purpose, the current radius of curvature of the path followedby the vehicle is calculated from the yaw rate and the measured drivingspeed. It may be assumed in first approximation that the shape of thecurve of the vehicle's traffic lane corresponds to an arc having thisradius. For the purpose of refinement, changes in the radius ofcurvature when entering or exiting a curve may be used forextrapolation, if necessary in combination with the measured lateralmovements of the vehicles ahead.

The locating data for the selected target object is transmitted to ACCmodule 10, together with the measured speed of the vehicle, and thereforms the basis for speed or distance regulation. If a target objectsuch as a vehicle ahead is in the same lane, then the speed is reducedto a value below the desired speed selected by the driver in order toguarantee that the target object will be tracked at a safe,speed-dependent distance.

A monitoring module 24 is used to check continuously, by reference tothe measured locating data and to known and/or measured vehicleperformance parameters, whether the conditions for safe operation of theACC system continue to exist. If this is not the case, such as when thetracked target object decelerates so abruptly that the maximumdeceleration of the vehicle that can be achieved using the ACC system isnot sufficient to maintain the desired distance so that activeintervention by the driver is required, monitoring module 24 issues amanual takeover prompt to the driver via a speaker 26. This takeoverprompt, which alerts the driver to the fact that the driver's activeintervention in the driving process is required, may consist of acharacteristic acoustic signal, for example. If the vehicle has anavigation system with voice output, the takeover prompt may also be aspoken instruction. Optionally or additionally, the takeover prompt mayalso be an optical signal, such as a blinking indicator light on thedashboard or the like.

FIG. 2 schematically shows a roadway having two traffic lanes 28, 30, inwhich a vehicle 32 equipped with an ACC system as shown in FIG. 1 (inthe right-hand traffic lane 30) and three vehicles ahead 34, 36 and 38are traveling. Detection range 40 of locating system 16, i.e., the rangescanned by the radar beam of the radar sensor, is indicated by hatching.All three vehicles ahead 34, 36 and 38 are within detection range 40 sothat their locating data is measured by locating system 16. Vehicles 34and 36 are in the same traffic lane 30 as vehicle 32, while vehicle 38is in adjacent traffic lane 28. Under these conditions, evaluationdevice 18 will select vehicle 34 as the target object.

As shown in FIG. 2, detection range 40 emanates in the shape of a fanfrom vehicle 32 and does not attain a width that correspondsapproximately to the width of traffic lane 30 until a distance isreached that corresponds more or less to the distance to vehicle 34.Within the speed range in which the ACC system is normally operated(e.g. above 20 km/h), the usual margin of safety between vehicles (andtherefore also the distance from target object 34) is so great that thetarget object is always within detection range 40 and may therefore bereliably detected. If, however, the speeds of the vehicles and also thedistances between the vehicles are reduced in a traffic jam, a certainlateral offset of vehicles within the same traffic lane may cause thetarget object to disappear from detection range 40. This would be thecase in FIG. 2, for example, where position 34′ of the target object isshown by a broken line. Without additional safety measures, this wouldresult in a situation in which evaluation device 18 now selects vehicle36 as the new target object and the ACC module regulates the speed sothat vehicle 32 drives closer to vehicle 36. In this situation, acollision with the vehicle in position 34′, which is no longer detected,could result.

The ACC system according to the present invention is designed so that italways remains in operation, even at low vehicle speeds down to speed 0.In order to avoid the danger of a collision, monitoring module 24 hasthe function of detecting target objects such as the one shown in FIG. 2by position 34′ and, upon detecting such a potentially dangeroussituation, issuing a manual takeover prompt.

Other situations that are detected by monitoring module 24 areillustrated in FIG. 3. This figure shows a curved roadway 42. Thepositions of vehicles 32 and 34 are shown in bold lines while they areentering a curve that gradually becomes tighter. Due to the curvature ofroad 42, vehicle 34 has migrated to the left edge of detection range 40.This migration is tracked by evaluation device 18 by reference to thechange in the associated azimuth angle. On the basis of this azimuthangle alone, however, it is not possible to determine whether vehicle 34has entered a curve or has changed lanes. However, the signal of yawrate sensor 22 indicates, as supplementary information, that vehicle 32has also already entered the curve. This points to the fact that therehas been no change of lanes, and that vehicle 34 is continuing to travelin the same lane as vehicle 32. On the basis of the continuing change inthe azimuth angle of vehicle 34, it is to be expected that this vehicle,as it travels further into the curve, will migrate out of detectionrange 40 or detection range 40 a, which is illustrated in conjunctionwith vehicle positions 32 a and 34 a, which are shown by thinner lines.For this reason, the manual takeover prompt will also be issued to thedriver in this situation. It is not necessary in this case to wait untilvehicle 34 has actually left the detection range.

Positions 32 b and 34 b in FIG. 3 illustrate a situation in which,similar to FIG. 2, the vehicle ahead will disappear from the detectionrange if vehicle 32, which is equipped with the ACC system, approachesmore closely. In this situation in FIG. 3, the target object will alsobe lost even if the distance is unchanged because the two vehicles exitfrom the curve and in the process detection range 40 b is rotatedrelative to the target object in such a way that the vehicle ahead is nolonger detected. Monitoring module 24 detects, by reference to thesignal from yaw rate sensor 22, that the vehicle is traveling along aleft-hand curve and, by reference to the locating data, that the targetobject is migrating to the right-hand edge of the detection range. This,too, results in the output of a takeover prompt.

FIG. 3 shows, furthermore, that as the vehicle is traveling along thecurve, detection range 40 a no longer overlaps very much at all with thetraffic lane in which the vehicle is traveling. This problem, i.e.,vehicles ahead get lost temporarily in a curve, also occurs in the caseof standard ACC regulation at higher speeds and at greater vehicledistances, but is less serious in those cases because the curve radii ofexpressways and superhighways are generally very large and because thevehicle ahead will certainly be detected again by the radar beam as soonas the vehicles exit from the curve. When speeds are lower and thedistances smaller and, in particular, when traveling on country roadshaving tighter curves, it may happen, on the other hand, that thevehicle ahead is lost in the curve and that the distance has beenreduced to such an extent that, even before the vehicles exit again fromthe curve, the vehicle ahead is now in a blind spot outside thedetection range. At a low vehicle speed, it is therefore generallyadvisable to issue a takeover prompt when the measured curve radius isso small that the detection range is no longer able to cover asufficiently large portion of the vehicle's traffic lane.

FIG. 4 shows a flow chart of an example of a monitoring routine by whichthe functions of monitoring module 24, as described above, may beimplemented. The monitoring routine is called up periodically (S1),using a cycle time on the order of magnitude of several milliseconds,for example. As an option, the call of the monitoring routine may beomitted if the measured speed of the vehicle is above a defined value,such as above 60 km/h. In step S2, a decision is made based on the curveradius determined using the signal of yaw rate sensor 22 as to whetherthe detection range adequately covers the vehicle's traffic lane. Ifthis is not the case, the takeover prompt is issued immediately (S3). Ifsufficient coverage exists (curve radius is greater than a specificthreshold value), then in step S4 the system checks to determine, byreference to the locating data previously transmitted by evaluationdevice 18, whether a target object was still present in the precedingcycle of the monitoring routine. If this was not the case—because thetarget object that caused the speed to be reduced has already been lostearlier due to a lane change, for example—then the program is terminatedwith step S5, without a takeover prompt being issued.

If the presence of a target object was established in step S4, then instep S6 the system checks to determine whether the last measureddistance d from this target object to the vehicle is smaller than aspecified threshold value dmin. If distance d is greater than thisvalue, then the detection range at the location of the target object isso wide that it would only be possible for the target object to be lostif it leaves the vehicle's traffic lane. Under these conditions, notakeover prompt is required, and the program is again terminated withstep S5. The value dmin may be 20 m, for example; however, it may alsobe varied as a function of the curve radius calculated in step S2.

If a smaller distance from the target object has been established, thena check is made in step S7 by reference to the locating data transmittedfrom evaluation device 18, and also by reference to the speed and yawrate data, to determine whether one of the situations illustrated inFIG. 3 by bold or broken lines is present, i.e., situations in whichmigration of the target object out of the detection range is imminent.In this case, the program jumps to step S3, and the takeover prompt isissued.

Otherwise, a check is made in step S8 to determine whether the targetobject has actually been lost. If this is not the case, then this targetobject may continue to be tracked, and the program is terminated withstep S5 without a takeover prompt.

If, on the other hand, the target object was lost, then a check is madein step S9 to determine whether the difference between theabove-mentioned evaluation numbers Pi and Pa is greater than a specificthreshold value Th. If this difference is greater than the thresholdvalue, then this means that the target object was with maximumprobability in the vehicle's traffic lane immediately before it waslost, and therefore it is to be expected that it is still in thevehicle's traffic lane. In this case, therefore, the program branchesoff to the takeover prompt in step S3. If, on the other hand, thedifference between Pi and Pa is not greater than the threshold value,then the cause of the disappearance of the target object is determinedto be that the vehicle ahead has changed lanes. In this case, speedregulation may therefore be continued, and the program is terminatedwith step S5, again without a takeover prompt.

In all the cases in which the takeover prompt was issued in step S3, theprogram is then terminated with step S5.

Although the evaluation numbers Pi and Pa are measures of theprobability that the vehicle is in or outside its own traffic lane,these evaluation numbers do not need to be normalized so that theirtotal is always equal to 1. Since different criteria may be used undercertain conditions for determining the evaluation numbers Pi and Pa,their total may vary depending on the situation. Instead of evaluatingthe difference between Pi and Pa, the evaluation in step S6 may also bemade by forming the ratio of these evaluation numbers or by using someother algorithm that ensures that direct branching to step S5 will onlyoccur if it is possible to conclude with great certainty that the targetobject has left the vehicle's lane.

Another possible modification involves switching around the sequence ofsteps S6 and S7.

Furthermore, other criteria for a situation in which the target objectsexit from the detection range is imminent may also be checked in stepS7. Such a criterion might be, for example, that the target object has,on a straight road, a lateral offset from the vehicle that differs from0 but still within the vehicle's traffic lane (the check is analogous tostep S9) and in the target object's coming closer due to the decrease inthe distance from the left or right boundary of the detection range.

For the decision as to whether the target object has left the vehicle'straffic lane (step S9), the change in the lateral offset that wasmeasured in the past may also be tracked, if necessary, and extrapolatedto the future.

In a modified embodiment, the takeover prompt may be followed by furthermeasures that ensure that the driver reacts to the takeover prompt. Sucha measure may be, for example, the forcible reduction in speed, afterexpiration of a certain waiting time after the takeover prompt, if thedriver has not operated the gas pedal or the brake in the interim.

1. A speed controller for a motor vehicle, comprising: a locating systemfor detecting locating data for an object that is in front of thevehicle; an evaluation device for determining whether a detected objectneeds to be treated as a relevant target object in the vehicle's trafficlane; a monitoring module configured to detect, with the aid of thelocating data, a situation in which a danger exists that an object notdetected by the locating system is within a predetermined range,wherein, in this situation, the monitoring module triggers a takeoverprompt to a driver of the vehicle; and a control arrangement configuredto act on at least one of a drive system and a braking system of thevehicle, when a stationary target object is detected, so that thevehicle is automatically decelerated to a standstill; wherein theevaluation device is configured to calculate, with the aid of thelocating data, at least two evaluation numbers that specify theprobability that the target object is in the vehicle's traffic lane, andwherein, in the event of one of an imminent loss and actual loss of thetarget object from the detection range of the locating system, themonitoring module determines, with the aid of the two evaluationnumbers, whether the target object has one of left the vehicle's trafficlane and is still in the vehicle's traffic lane, and if the targetobject is still in the vehicle's traffic lane, triggers the takeoverprompt; wherein the calculation of the at least two evaluation numbersincludes: a) calculating for each detected object, using the locatingdata with the aid of trigonometric functions, a lateral offset in adirection perpendicular to the direction of travel of the vehicle,wherein the locating data includes measured distance to the detectedobject and azimuth angle of the detected object relative to thedirection of travel of the vehicle; and b) comparing the lateral offsetto a known, typical width of a lane, whereby the at least two evaluationnumbers are derived, the at least two evaluation numbers including afirst probability value corresponding to the detected object being inthe lane of the vehicle and a second probability value corresponding tothe detected object being outside of the lane of the vehicle.
 2. Thespeed controller according to claim 1, wherein the monitoring moduleonly triggers the takeover prompt if a distance of the target objectfrom the vehicle is smaller than a specified threshold value.
 3. Thespeed controller according to claim 2, wherein the evaluation devicedetermines, with the aid of an output signal of at least one sensor,whether the vehicle is traveling along a curve, and if the vehicle istraveling along a curve, calculates a curve radius, and wherein themonitoring module also evaluates the curve radius in addition to thelocating data in detecting a situation in which danger exists.
 4. Thespeed controller according to claim 3, wherein the monitoring modulevaries the threshold value as a function of the curve radius.
 5. Thespeed controller according to claim 3, wherein the monitoring moduletriggers the takeover prompt independent of whether a target object hasbeen detected, if the curve radius is smaller than a predefined value.6. The speed controller according to claim 1, wherein the locatingsystem is a radar sensor.
 7. The speed controller according to claim 1,wherein the takeover prompt is an acoustic signal generated by aspeaker.